1. Field of the Invention
The invention relates generally to the field of agriculture. More specifically, the invention relates to methods for improving plant health by application of dicamba herbicide and/or metabolites or analogs thereof to plants.
2. Description of Related Art
Dicamba (3,6-dichloro-o-anisic acid or 3,6-dichloro-2-methoxybenzoic acid; FIG. 7), active ingredient in herbicides such as Banvel® (BASF), Clarity® (BASF), and Vanquish® (Syngenta), is a potent herbicide. Although its precise mechanism of activity is unclear, it appears to act as a plant growth regulator (e.g. Grossmann 2000). Its application results in uncontrolled growth, leaf curling and twisting, chloroplast damage, and direct phytotoxic effects, among others. Some of these effects are believed to be caused by ethylene synthesis, which triggers an increase in the biosynthesis of abscisic acid, another plant hormone. Thus imbalances in plant hormone levels appear to underlie the toxic effects.
A dicamba monooxygenase (DMO), has been found to confer tolerance to dicamba by degrading it to 3,6-dichloro salicylic acid (DCSA; 3,6-DCSA; FIG. 7) in bacteria (e.g. Herman et al., 2005; US Patent Publ. 20060168700; U.S. Pat. No. 7,022,896). The DMO gene has subsequently been used to confer tolerance to Dicamba in soybean and other plants (e.g. Weeks et al., 2006). These new dicamba-tolerant crops allow for applications of dicamba on crops which were previously extremely sensitive to any dicamba exposure, particularly dicots such as cotton, canola, and soybean.
U.S. Pat. No. 7,230,163 describes a method of improving crop yields by application of a synthetic auxin to a plant. However, plant health, e.g. resistance to biotic or abiotic stress, is not addressed, nor is the effect of metabolites of the applied auxin.
As in planta metabolism is generally unpredictable, i.e., one cannot predict from prior traditional uses of dicamba (e.g., on corn not expressing a DMO gene) what metabolites might result from the use of dicamba in new dicamba-tolerant crops expressing DMO, or the effects of such metabolites in the plant. The present inventors have found that in these DMO-expressing crops, DMO detoxifies dicamba and produces dicamba metabolites, including DCSA. Unexpectedly, the present inventors have also discovered that this DCSA metabolite confers beneficial health effects on the plants. Accordingly, the present invention is directed to, among other things, methods of improving plant health using dicamba metabolites, including DCSA, and the plants, seeds, and crops resulting therefrom.
These improvements in plant health provide increased resistance of plants against biotic (e.g., insects, fungi, viruses, nematodes, and other pathogens) and abiotic stresses (e.g., drought, cold, ozone, soil nutrient deficiencies), with resulting increases in yields and improved quality of crops, all of which will be a great benefit to agriculture.